This invention relates, in general, to coating applicator systems and, more particularly, their use in an improved photoelectrophoretic imaging system.
In the photoelectrophoretic imaging process, monochromatic including black and white or full color images, are formed through the use of photoelectrophoresis. An extensive and detailed description of the photoelectrophoretic process is found in U.S. Pat. Nos. 3,384,488 and 3,383,565, to Tulagin and Carreira; 3,383,993 to Yeh and 3,384,566 to Clark, which discloses a system where photoelectrophoretic particles migrate in image configuration providing a visible image at one or both of two electrodes between which the particles suspended within an insulating carrier is placed. The particles are electrically photosensitive and are believed to bear an electrical charge while suspended, which causes them to be attracted to one electrode and apparently undergo a net change in polarity upon exposure to activating electromagnetic radiation. The particles will migrate from one of the electrodes under the influence of an electric field through the liquid carrier to the other electrode.
The photoelectrophoretic imaging process is either monochromatic or polychromatic, depending upon whether the photosensitive particles within the liquid carrier are responsive to the same or different portions of the light spectrum. A full-color polychromatic system is obtained, for example, by using cyan, magenta and yellow colored particles which are responsive to red, green and blue light, respectively.
In photoelectrophoretic imaging generally, and as employed in the instant invention, the important broad teachings in the following four paragraphs should be noted.
Preferably, as taught in the four patents referred to above, the electric field across the imaging suspension is applied between electrodes having certain preferred properties, i.e., an injecting electrode and blocking electrode, and the exposure to activating radiation occurs simultaneously with field application. With respect to the application of the electrical field, it should be noted that various of the four patents referred to above and, additionally, Luebbe et al., U.S. Pat. No. 3,595,770; Keller et al., U.S. Pat. No. 3,647,659 and Carreira et al., U.S. Pat. No. 3,477,934 teach a wide variety of materials and techniques for associating an electrical bias with the materials, e.g., charged insulating webs. Accordingly, it should be understood that opposed electrodes generally may comprise the means for applying the electrical field across the imaging suspension. In preferred embodiments herein, one electrode is referred to as the injecting electrode and the other electrode as the blocking electrode. The terms injecting electrode and blocking electrode should be understood and interpreted in the context of the above comments throughout the specification and the claims.
It should also be noted that any suitable electrically photosensitive particles may be used. Kaprelian, U.S. Pat. No. 2,940,847 and Yeh, U.S. Pat. No. 3,681,064, disclose various electrically photosensitive particles, as do the four patents referred to above.
In a preferred mode, at least one of the electrodes is transparent. In this embodiment, the electrode may be completely or substantially completely transparent or it may be only partially transparent yet transmit enough activating radiation to allow photoelectrophoretic imaging to occur. In another embodiment, such as is described in Weigl, U.S. Pat. No. 3,616,390, both electrodes may be opaque.
In operation, preferably the injecting electrode is grounded and the blocking electrode is biased to provide the electrical field for imaging. However, it should be noted that a wide variety of variations in how the electrical field may be applied can be used. These include, for example, grounding the blocking electrode and biasing the injecting electrode; biasing both electrodes with different bias values of the same polarity; biasing one electrode at one polarity and biasing the other electrode at the opposite polarity of the same or different magnitude, etc. Generally, any suitable technique for establishing an electrical field across the imaging suspension may be used.
The electrode used in the photoelectrophoretic imaging system may be provided in a variety of configurations including flat plates, rollers, endless belts, etc.